This application is based on application No. 10-2000-30429 and No. 10-2001-29563 filed in the Korean Industrial Property Office on Jun. 2, 2000, and May 29, 2001 respectively, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a remover of dissolved fluoride ion for removing fluoride ions contained in wastewater and a treatment method for wastewater containing fluoride ions using the same. More particularly, the present invention relates to a new treatment method, wherein not only a very small amount of fluoride ion can be efficiently removed but also the whole of the sludge generated from the process can be reused by adding calcium carbonate as main material, poly sodium phosphate, and active aluminum to form a very stable precipitate.
2. Description of the Related Art
The usual treatment method for wastewater containing fluoride ion, which is generated from all kinds of semiconductor manufactories, electrolyzing and refining aluminum factories, metal surface-treating factories, print-substrate manufactories, and ceramic manufactories, has been where fluoride ion is made to be an insoluble material by adding at least one or more compounds selected from a group composed of calcium compound, aluminum compound, and phosphorus compound to the wastewater containing fluoride, and then removing the insoluble materials by a solid-liquid separation.
The representative method among the above methods is disclosed in Japanese Patent Publication Number Showha 60-117 using a combination of aluminum compound as aluminum sulfate and calcium compound as calcium hydroxide, and in Japanese Patent Publication Number Showha 62-125894 using a combination calcium compound such as calcium chloride and phosphorus compound such as potassium phosphate.
For example, in a semiconductor manufactory where the treatment method involves wastewater containing fluoride of 300xcx9c600 ppm collected into a water-collection tank, the pH in 1st reaction tank is controlled to be about 10 by adding calcium hydroxide, a small amount of iron chloride(III)(CaCl2) as a support flocculent is added to 2nd reaction tank, the fluoride concentration is brought down to 30xcx9c60 ppm by adding a polymer flocculent in 3rd reaction tank to change the fluorides to calcium fluoride which is removed by precipitation-separating in 1st precipitation tank. Furthermore, the filtrate is transported to 1st precipitation-reaction tank and injected with poly aluminum chloride (PAC) of about 600 ppm, pH in 2nd precipitation-reaction tank is controlled between 6.7xcx9c7.0 with sodium hydroxide input. After then, the fluoride concentration is brought down to a level of below 10 ppm by adding polymer flocculent in 3rd precipitation-reaction tank, and the residual fluoride is removed by precipitation-separating in 2nd precipitation tank, as shown in the process diagram of FIG. 1.
However, the method is very complex because the fluoride treatment method involves a 2-step process that should perform filtration-separation twice. Furthermore, it is very difficult to operate, handle and maintain the equipment of performing precipitation and filtration twice, requiring a lengthy time, and more important is the fact that there is much difficulty in treating the large amount of sludge generated from the wastewater treatment process.
The object of the present invention is to consider the problems of the prior art, and to provide an improved removing agent of dissolved fluoride ion that is able to selectively remove fluoride ions to result in a low concentration of wastewater containing fluoride ion by only a one-step treatment, regardless of the initial concentration and treatment methods for wastewater comprising fluoride using the same.
In order to achieve the above objects, the present invention provides a remover of dissolved fluoride ions comprising:
a) hydrochloric acid solution reacted with calcium carbonate.
Furthermore, the remover of dissolved fluoride ion can also comprise:
b) a mixture of poly sodium metaphosphate and active aluminum or aqueous solution of mixtures thereof, or an aqueous solution of rare earth element.
The present invention also provides a treatment method for wastewater containing fluorides comprising the step of:
a) adding hydrochloric acid solution reacted with calcium carbonate to the wastewater containing fluorides.
Furthermore, the treatment method for wastewater containing fluoride can also comprise the following step of:
b) controlling pH of the wastewater above pH 5.0 by adding alkali solution to the wastewater of a) step.
Furthermore, the treatment method for wastewater containing fluoride can also comprise the following step of:
c) adding a mixture of poly sodium metaphosphate and active aluminum or aqueous solution of mixtures thereof, or an aqueous solution of rare earth element to the waste water of b) step until the pH of wastewater is 4.0xcx9c10.0, and then adding the prescribed polymer flocculent.
Furthermore, the treatment method for the wastewater containing fluoride can also comprise the following step of:
d) separating the generated sludge from a) step through to c) step from the mixed solid-liquid phase, and then discharging the wastewater of liquid phase.
Furthermore, the treatment method for wastewater containing fluoride can also comprise the following step of:
e) reusing the separated solid sludge of d) step as a material for cement.